JPH0514313A - Automatic gain control circuit - Google Patents

Abstract

PURPOSE:To eliminate the effect of phase fluctuation by using one correlation device to realize a flat correlation characteristic in the vicinity of a synchronization point and using its output for a gain control signal. CONSTITUTION:An information signal controls an oscillating frequency of a voltage controlled oscillator 1 at a sender side and an output of the said voltage controlled oscillator 1 is used for a clock signal to drive a PN code generator 2, which generate a PN code. The output of the said PN code generator 2 is divided into two, the only one is fed to a delay circuit 3, in which the signal is delayed by one tip and fed to an adder 4, in which a sum signal from the delayed signal and the other signal is generated and the sum signal is used as a transmission signal. A gain control amplifier 5 amplifies the received signal at first a receiver side, an output of the said gain control amplifier 5 is divided into two, the one is used for synchronization and demodulation of the PN code. The other output is multiplied with a synchronized PN code from a synchronization demodulation section at a multiplier 9, the product is given to a low pass filter 10, from which only the DC component is extracted and it is used for a control signal for the gain control amplifier 5.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an automatic gain control circuit in a spread spectrum communication system. For example, it is applied to spread spectrum communication and wireless communication.

[0002]

2. Description of the Related Art As a known document describing the prior art of the present invention, there is, for example, Japanese Patent Laid-Open No. 61-93745. The "spread spectrum transmitter / receiver" of this publication changes the oscillation frequency of a voltage-controlled oscillator with an information signal and uses this oscillation signal as a clock for generating pseudo noise by a pseudo noise generator, and at the same time, generates the oscillation signal and the pseudo noise. With the spread spectrum, the signal is transmitted, and the receiving section forms a loop with a correlation detector, bandpass filter, voltage controlled oscillator, pseudo noise generator, etc., which has a simpler configuration than before and is less susceptible to DC drift. It was done.
However, since the autocorrelation characteristic of the PN code is used for the gain control signal, the correlation characteristic has a triangular shape.
If there is a phase variation, there is a drawback that the amplification gain of the received signal also varies.

As a method of preventing this, two PN codes that are time-shifted by one chip are prepared on the receiving side, the correlation with each received signal is obtained by a correlator, and the sum of the two is used as a gain control signal. This makes it possible to flatten the correlation characteristic in the vicinity of the synchronization point and obtain a gain control signal that is not affected by phase fluctuations. However, as a new problem, when there is some asymmetry in the circuit, the two signals are out of balance, and the phase variation also causes a variation in the amplification gain of the received signal.

FIGS. 4A to 4C are block diagrams of the conventional spread spectrum transmitter / receiver described in the above publication.
FIG. 7A is a transmitter, FIG. 8B is a receiver, and FIG. 8C is a diagram showing correlation characteristics. In the figure, 31 is a voltage controlled oscillator, 3
2 is a frequency divider, 33 is a PN code generator, 34 is a multiplier, 3
5 is a gain control amplifier, 36 is a correlation detector, 37 is a voltage controlled oscillator, 38 is a PN code generator, 39 is a multiplier, 40
Is a band pass filter (BPF), and 41 is a detector.

On the transmission side of FIG. 1A, the output of the voltage controlled oscillator 31 is divided by a frequency divider 32, and the PN code generator 33 is driven by the output of the frequency divider 32 to generate the PN code. The output of the multiplier 33 and the output of the voltage controlled oscillator 31 are multiplied by the multiplier 3
4 is used as a transmission signal. On the other hand, on the receiving side, after the received signal is amplified by the gain control amplifier 35, a PN code synchronized with the received signal is generated by the synchronous demodulation unit, and the PN code generator 38 and the amplified received signal are multiplied by the multiplier 39. The signal amplitude is obtained by the detector 41 for the band pass filter (BPF) 40, and the gain control of the gain control amplifier 35 is performed by using the output of the detector 41 as a control signal. There is. At this time, since the correlation of the same code is obtained in the despreading process, the correlation characteristic has a triangular shape as shown in FIG. Since the synchronization point is at the peak point, the correlation value becomes small regardless of whether the phase of the synchronization point is advanced or delayed, which causes fluctuation in the control signal.

[0006]

[Object] The present invention has been made in view of the above-described circumstances, and by devising the spread signal itself, one correlator realizes a flat correlation characteristic in the vicinity of the synchronization point, and gain control By providing a gain control circuit that is not affected by phase fluctuations by using it for a signal, and with respect to the conventional method using two correlators, there is no need to consider the circuit balance, and The circuit configuration is greatly simplified by becoming one, and the peak part of the correlation characteristic is flattened by discriminating the transmission spread signal or the reception spread signal, and the fluctuation of the correlation characteristic due to the phase fluctuation. It is an object of the present invention to provide an automatic gain control circuit which eliminates the above and stabilizes the gain control.

[0007]

In order to achieve the above object, the present invention provides (1)
A voltage-controlled oscillator whose oscillation frequency is controlled by an information signal, a pseudo-noise code generator that generates a pseudo-noise code using the output of the voltage-controlled oscillator as a clock signal, and an output signal of the pseudo-noise code generator A delay circuit for inputting one output signal and an adder for inputting the output of the delay circuit and the other half of the output signal of the pseudo-noise code generator for inputting as a transmission signal. A transmission circuit, a gain control amplifier that amplifies the transmission signal from the transmission circuit as a reception signal, an output signal of the gain control amplifier, and a correlation between an output signal from the same pseudo noise code generator as the transmission circuit. A receiving circuit composed of a correlator for calculation and a low-pass filter for passing only the DC component of the correlation output of the correlator and outputting the control signal of the gain control amplifier; or (2) A voltage-controlled oscillator whose oscillation frequency is controlled by a report signal, a pseudo-noise code generator that generates a pseudo-noise code using the output of the voltage-controlled oscillator as a clock signal, and an output signal of the pseudo-noise code generator are divided into two. ,
A delay circuit for inputting one output signal, an adder for inputting the output of the delay circuit and the other half of the output signal of the pseudo noise code generator, an output of the adder and the voltage A transmission circuit comprising a multiplier for multiplying the output of the controlled oscillator into a transmission signal, a gain control amplifier for amplifying the transmission signal from the transmission circuit as a reception signal, an output signal of the gain control amplifier and the transmission A correlator that calculates the correlation with the output signal from the same pseudo-noise code generator as the circuit, a band-pass filter that passes only the carrier component of the correlation output of the correlator, and the output of the band-pass filter is detected. A receiver circuit comprising a detector for outputting a control signal of the gain control amplifier, and (3) the signal modulated by the information signal in (1) or (2) is divided into two parts. Then Instead of passing the signal through a delay circuit and then adding them again, a signal having a narrower signal transmission time width within one chip time of the pseudo noise code is used as the transmission signal, and further, (4) above (1), The circuit portion of the pseudo noise code generator, the delay circuit, and the adder in the transmission circuit of (2) or (3) or the code generation circuit portion in which the transmission time width of the signal within one chip time of the pseudo noise code is narrowed is received. It is characterized by being configured by a pseudo noise code generator on the side. Hereinafter, description will be given based on examples of the present invention.

1 (a) to 1 (c) are configuration diagrams for explaining an embodiment of an automatic gain control circuit according to the present invention. FIG. 1 (a) is a transmitter (transmission circuit) and FIG. 1 (b). Is a receiver (reception circuit), and FIG. 7C is a diagram showing correlation characteristics. 1 in the figure
Is a voltage controlled oscillator, 2 is a PN code generator, 3 is a delay circuit, 4 is an adder, 5 is a gain control amplifier, 6 is a correlator, and 7
Is a voltage controlled oscillator, 8 is a PN code generator, 9 is a multiplier,
Reference numeral 10 is a low pass filter (LPF). When the M sequence is used as the PN code, its autocorrelation characteristic is shown in FIG.
It becomes like (c). Therefore, P
When the values obtained by shifting the N code by ± 1/2 chip are added and the correlation with the original PN code is obtained, the characteristic becomes a trapezoidal shape as shown in FIG. An embodiment (claim 1) shown in FIG. 1 uses this correlation output for gain control. On the transmission side in FIG. 3A, the voltage-controlled oscillator 1
Of the voltage controlled oscillator 1 is used as a clock signal to drive a PN code generator 2 to generate a PN code. Then, the output of the PN code generator 2 is set to 2
Then, only one of them is passed through the delay circuit 3 to be delayed by one chip, and then input to the adder 4 to generate a sum signal of the two, which is used as a transmission signal. When the output of the PN code generator 2 is ± 1, the transmission signal has three values ± 2 and 0.

On the receiving side, first, the gain control amplifier 5
The received signal is amplified at 2, the output of the gain control amplifier 5 is divided into two, and one is used for synchronization and demodulation of the PN code. The other output is multiplied by the synchronized PN code from the synchronous demodulation unit by the multiplier 9, and the low-pass filter 10 extracts only the DC component and becomes the control signal of the gain control amplifier 5. The characteristics of the gain control signal are shown in FIG.
Because of the trapezoidal shape as shown in (c), the gain control amplifier 5 is not affected even if some phase fluctuation occurs near the delay amount 0. Although the delay amount of the delay circuit 3 is just one chip in this embodiment, the delay amount is not limited to this value. However, even if the delay amount is further reduced or increased, the area where the correlation output is flat decreases.

FIG. 2 is a diagram showing another embodiment of the automatic gain control circuit according to the present invention. In the figure, 11 is a frequency divider, 12 is a multiplier, 13 is a band pass filter (BPF), and 14 is detection. Other parts that have the same functions as those in FIG. 1 are denoted by the same reference numerals. The difference from the embodiment of FIG. 1 is that, on the transmission side, the output of the voltage controlled oscillator 1 is frequency-divided by a frequency divider 11, and the PN code driven by using the output of the frequency divider 11 as a clock signal is used as the voltage controlled oscillator. The point is that the output of 1 is multiplied to form a transmission signal. Therefore, the transmission signal can be transferred to the wireless band, and the present invention can be applied to wireless communication. On the receiving side, the received signal amplified by the gain control amplifier 5 corresponding to this is multiplied by the PN code generated in the synchronous demodulation section by this using the multiplier 9 and despread by the band pass filter 13. Only the carrier wave component is taken out and detected by the detector 14 to be the gain control signal of the gain control amplifier 5.

3 (a) and 3 (b) are views showing still another embodiment (claim 3) of the automatic gain control circuit according to the present invention. FIG. 3 (a) is a transmitter, and FIG. It is a figure which shows a correlation characteristic. In the figure, 21 is a voltage controlled oscillator, 22 is a PN code generator, and 23 is a switch. Instead of using the code having the cross-correlation characteristic of FIG. 1C, the code having the cross-correlation characteristic of FIG. 3B is used. This code is obtained by outputting a normal PN code for only half a cycle of the drive clock. The ± 1 output from the PN code generator 22 is input to the switch 23, and the O of the switch 23 is turned on by the code clock.
It is sufficient to control N and OFF. As the switch 23, various types such as transistors and FETs can be considered. Figure 1,
By using the circuit of FIG. 3 instead of the delay circuit 3 and the adder 4 in FIG. 2, the cross-correlation characteristic of FIG. 3B can be obtained, and a gain control signal that is not affected by the delay time can be obtained. I can. In addition, here, the output is a half cycle of the clock,
The present invention is not limited to this, and the shorter the output period is, the wider the range where the correlation output shows a peak and the lower the peak value are.

Next, the invention of claim 4 is the one in which the PN codes on the transmitting side and the receiving side in the invention described in claims 1 to 3 are interchanged, and is effective when it is desired to simplify the circuit configuration on the transmitting side. is there. Although all of the above examples have described the transmitter / receiver of the type that modulates the drive clock frequency of the PN code, the modulation / demodulation method may be amplitude modulation, phase modulation, or the like, and the present invention can be applied to these. Of course. There is no need for modulation if only synchronization is required. Further, as the transmission medium, radio waves, light, etc. can be used in addition to the wired communication.

[0013]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: A PN code is generated on the transmitting side, its output signal is divided into two, one is passed through a delay circuit, and then the summed signal and the PN code on the receiving side are added. Since the gain control signal is obtained by calculating the correlation and passing the correlation output through the LPF that passes only the DC component, the correlation value can operate in a constant region, and the gain of the amplifier is affected by the phase fluctuation between the PN codes between the transmitter and the receiver. Do not receive (2) Effect corresponding to claim 2: A PN code is generated on the transmission side, the output signal is divided into two, one is passed through a delay circuit, then added again, and the carrier is multiplied by a multiplier. The correlation between the signal and the PN code on the receiving side is obtained, and the correlation output is detected by passing it through the BPF that passes only the carrier band, and the gain control signal is used. Therefore, the correlation value can operate in a constant region and the gain of the amplifier can be increased. It is not affected by the phase fluctuation between PN codes between the transmitter and the receiver. (3) Effect corresponding to claim 3: Instead of halving a signal modulated by an information signal and passing one through a delay circuit and then adding them again, transmission of the signal within one chip time of the PN code Since the signal whose time width is narrowed is used as the transmission signal, the same effects as those of claims 1 and 2 can be obtained by only adding a very simple circuit. Moreover, since there is a time when no signal is transmitted, the transmission power can be reduced. (4) Effect corresponding to claim 4: The fact that the same function and effect are obtained even if the codes in the inventions of claims 1 to 3 are exchanged between the transmitter and the receiver is utilized, and the degree of freedom in circuit design is increased. Can be increased.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of an automatic gain control circuit according to the present invention.

FIG. 2 is a configuration diagram for explaining another embodiment of the automatic gain control circuit according to the present invention.

FIG. 3 is a configuration diagram for explaining still another embodiment of the automatic gain control circuit according to the present invention.

FIG. 4 is a block diagram of a conventional spread spectrum transmitter / receiver.

[Explanation of symbols]

1 ... Voltage controlled oscillator, 2 ... PN code generator, 3 ... Delay circuit, 4 ... Adder, 5 ... Gain control amplifier, 6 ... Correlator, 7
... voltage-controlled oscillator, 8 ... PN code generator, 9 ... multiplier,
10 ... Low-pass filter (LPF).

Claims (4)

[Claims] 1. A voltage-controlled oscillator whose oscillation frequency is controlled by an information signal, a pseudo-noise code generator that generates a pseudo-noise code using the output of the voltage-controlled oscillator as a clock signal, and an output of the pseudo-noise code generator. A signal is divided into two, and a delay circuit for inputting one of the output signals and an output of the delay circuit for inputting the other half of the output signal of the pseudo noise code generator are input as transmission signals. A transmission circuit including an adder, a gain control amplifier for amplifying a transmission signal from the transmission circuit as a reception signal, an output signal of the gain control amplifier, and an output from the same pseudo noise code generator as the transmission circuit. It has a receiving circuit including a correlator that calculates a correlation with a signal and a low-pass filter that passes only the DC component of the correlation output of the correlator and outputs the control signal of the gain control amplifier. Automatic gain control circuit as a characteristic. 2. A voltage controlled oscillator whose oscillation frequency is controlled by an information signal, a pseudo noise code generator which generates a pseudo noise code using the output of the voltage controlled oscillator as a clock signal, and an output of the pseudo noise code generator. A delay circuit that divides the signal into two and inputs one output signal; an adder that inputs the output of the delay circuit and the other divided output signal of the pseudo noise code generator; Circuit comprising a multiplier for multiplying the output of the voltage control oscillator and the output of the voltage controlled oscillator into a transmission signal, a gain control amplifier for amplifying the transmission signal from the transmission circuit as a reception signal, and the gain control amplifier A correlator for calculating the correlation between the output signal of the correlator and the output signal from the same pseudo-noise code generator as the transmission circuit, a band pass filter for passing only the carrier component of the correlation output of the correlator, and the band An automatic gain control circuit comprising a receiving circuit including a detector for detecting an output of a band pass filter and outputting a control signal of the gain control amplifier. 3. A signal transmission time width within one chip time of a pseudo noise code is narrowed instead of dividing a signal modulated by the information signal into two and passing one through a delay circuit and then adding them again. 3. The automatic gain control circuit according to claim 1, wherein the automatic gain control circuit is a transmission signal. 4. A code in which the transmission time width of a signal within one chip time of the pseudo noise code generator, delay circuit and adder in the transmission circuit of claim 1, 2 or 3 or the pseudo noise code is narrowed. The automatic gain control circuit is characterized in that the generation circuit part of is composed of a pseudo noise code generator on the receiving side.